U.S. patent application number 10/398390 was filed with the patent office on 2004-04-15 for piezoelectric extension actuator.
Invention is credited to Bebesel, Marius, Jaenker, Peter.
Application Number | 20040070311 10/398390 |
Document ID | / |
Family ID | 26007263 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040070311 |
Kind Code |
A1 |
Bebesel, Marius ; et
al. |
April 15, 2004 |
Piezoelectric extension actuator
Abstract
It is the object of the invention to create a piezoelectric
expansion actuator for d33 piezoelements, which allows vibrations
in structures to be suppressed. This object is achieved pursuant to
a solution of the invention in that the expansion actuator (1)
comprises a piezoelectric stack (2), which consists of d33
piezoelectric elements and is arranged between output elements (4),
which are attached to the surface of the structure (7). The
invention applies to a piezoelectric extension actuator, which is
used to control vibrations in structures. Another, alternative
solution is based on the damping of vibrations between the main
gearbox of a helicopter rotor and the cellular structure of the
cockpit. The power application point of the output element (18, 19,
180, 190; 35, 36) is arranged at a distance from the corresponding
end plate of the piezoelectric stack (22, 220; 31, 32, 33) in the
axial direction (X).
Inventors: |
Bebesel, Marius; (Munchen,
DE) ; Jaenker, Peter; (Garching, DE) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
26007263 |
Appl. No.: |
10/398390 |
Filed: |
November 7, 2003 |
PCT Filed: |
October 2, 2001 |
PCT NO: |
PCT/EP01/11360 |
Current U.S.
Class: |
310/311 |
Current CPC
Class: |
F16F 15/005 20130101;
B64C 2027/7283 20130101; Y02T 50/34 20130101; Y02T 50/30 20130101;
H02N 2/043 20130101 |
Class at
Publication: |
310/311 |
International
Class: |
H02N 002/00; H01L
041/04; H01L 041/08; H01L 041/18 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2000 |
DE |
100 49 176.6 |
Aug 11, 2001 |
DE |
101 39 686.4 |
Claims
1. Piezoelectric expansion actuator for reducing vibrations in
structures, wherein the expansion actuator (1) comprises a
piezoelectric stack 2 that is made of d33 piezoelectric elements
and is seated between output elements (4), which are attached to
the surface of the structure (7).
2. Expansion actuator pursuant to patent claim 1, wherein
mechanical precompression stress is applied on the piezoelectric
stack (2) by means of a prestress element (6).
3. Expansion actuator pursuant to patent claim 2, wherein the
prestress element (6) consists of one or more mechanical tension
springs.
4. Expansion actuator pursuant to patent claim 3, wherein the
prestress element (6) consists of elastic end plates (3), which
limit the piezoelectric stack (2) that is inserted in the output
elements (4) under pressure.
5. Expansion actuator pursuant to one of the patent claims 1
through 4, wherein in the expansion actuator (1) a stroke speed
transformation is integrated.
6. Expansion actuator pursuant to patent claim 5, wherein for the
purpose of achieving the stroke speed transformation in the output
elements (4) an inwardly open one-sided slot (9) that runs parallel
to the surface of the structure (7) and an elastic pressure web
(8), respectively, are arranged between the end plates (3) of the
piezoelectric stack (2) and the output surfaces (5) of the output
elements (4).
7. Expansion actuator pursuant to patent claim 5, wherein for the
purpose of achieving the stroke speed transformation the output
elements (4), respectively, are designed to include an articulating
lever (12), wherein behind a first lever section (13) the
piezoelectric stack (2) with an output web (14) engages the lever
(12) in an articulating manner and wherein behind a second lever
section (15) the support bar (11) engages the lever (12) in an
articulating manner.
8. Piezoelectric expansion actuator for reducing vibrations in
structures, wherein at least one piezoactuator is arranged on a
strut, which connects the main gearbox of a helicopter rotor with a
cellular structure of the cockpit, and the piezoactuator introduces
a controlled force in one section of the strut for the purpose of
elastic dimensional change of this section of the strut,
characterized in that the piezoactuator (17, 170; 34) comprises at
least one piezoelectric stack (22, 220; 31, 32, 33) made of d33
piezoelectric elements, which is seated between output elements
(18, 19, 180, 190; 35, 36) that are attached to the surface of the
structure (16; 30), wherein the resting surfaces (23, 24, 230, 240;
370, 380) of an output element are arranged on the strut at a
distance in relation of the corresponding end plate of the
piezoelectric stack (22, 220; 31, 32, 33) in the axial direction
(X).
9. Expansion actuator pursuant to patent claim 8, wherein the
output element (18, 19, 180, 190; 35, 36) forms a lever arm (E, F)
from its configuration on an end plate up to the power application
point.
10. Expansion actuator pursuant to patent claim 8, wherein the
distance (D) of the resting surfaces (23, 24, 230, 240) of the
output elements (18, 19, 180, 190) can be adjusted variably.
11. Expansion actuator pursuant to one of the claims 8, 9 or 10,
wherein the collar (400) of the output element (360) contains
recesses (401).
12. Expansion actuator pursuant to one of the claims 8, 9, 10 or
11, wherein the output element can be composed of sectional output
elements in a circumferential direction of the strut so that
retrofitting of an already installed strut is possible.
Description
[0001] The invention relates to a piezoelectric expansion actuator
pursuant to the preamble of Patent claim 1 and that of the
Subsidiary claim 8.
[0002] The use of d31 piezoplates or d31 piezosegments is known for
the purpose of vibration control and to influence vibrations in
structures. d31 piezoplates take advantage of the elastic
transverse contraction of the piezoelectric material. Several
piezoplates or piezosegments are described in the following in
summary as piezoelectric stacks. A piezoelectric stack consists of
several, but at least 2 piezoelements. With the above d31
piezoelements, for example, expansions are introduced into carrier
structures for helicopter transmissions so as to suppress the
transmission of body sound onto the helicopter cell. In doing so,
the d31 piezoelements are integrated in accordance with their
expansion direction, which acts parallel to the surface of the d31
elements, into the surface of the carrier structure across a large
surface, e.g. through an adhesion technique.
[0003] By contrast, the expansion in the familiar d33 piezoelements
acts perpendicular to the surface of the elements because d33
piezoplates take advantage of the expansion of the piezoelectric
material in the direction of the applied field.
[0004] DE 198 13 959 A1 is aimed at making a device for body sound
suppression available that more effectively reduces the
transmission of equipment vibrations and oscillations through a
carrier structure onto a cellular structure of a cockpit in a
simple construction and at relatively low integration complexity.
DE 198 13 959 A1 reveals that the device for body sound suppression
comprises at least one piezo-actuator, which introduces the
oscillations into the carrier structure in order to block the body
sound transmission path onto the insulating structure substantially
and to compensate acoustic excitation by means of the existing and
excited system dimensions of the sound generator more effectively.
This technical idea is not limited to use in helicopter
manufacturing. It can be employed in all areas of mechanical
engineering where a device for body sound suppression becomes
necessary.
[0005] Contrary to other familiar expansion actuators, the
piezoactuator implements the application of power onto the carrier
structure no longer in points, but rather across a relatively large
surface of the carrier structure. The carrier structure can be
arranged for example between the main gearbox of a rotor and a
cellular structure of the cockpit of a helicopter. In this case,
the carrier structure would be one or more struts (also called gear
struts). The piezoactuator is largely arranged along the entire
circumference of the strut and exhibits a defined expansion in the
axial direction of the strut. Forces are introduced by the
piezoactuator pursuant to DE 198 13 959 A1 via its surface.
[0006] The efficiency of power application is limited by the
effective surface of the strut that is to be covered.
[0007] The invention is based on the task of creating a
piezoelectric expansion actuator for d33 piezoelements, with which
vibrations can be suppressed in structures, and furthermore of
considerably increasing the efficiency of power application of a
piezoactuator despite the contrary tendency of decreasing
construction volume of the piezoactuator.
[0008] This task is resolved pursuant to the invention with the
features of patent claim 1 as well as alternatively with the
features of the subsidiary claim 8. Further developments of the
invention are provided in the dependent claims.
[0009] A solution pursuant to the invention is based on the fact
that a d33 piezoelement in the form of a stack is clamped into a
mechanical frame, which is fastened to the surface of the
structure. Apart from a highly specific, mechanical power, the
invented expansion actuator also achieves good efficiency. Also
beneficial is the application of mechanical pre-stress that is
integrated in the actuator and which allows critical tension strain
to be avoided for the piezoelements. Optionally, devices can be
integrated in the frame with which stroke speed transformations or
stiffness transformations can be beneficially achieved.
[0010] In another solution pursuant to the invention, the
efficiency of power application for the piezo actuator can be
improved by considerably increasing the distance between the
resting areas of two output elements of a piezoactuator and a
corresponding end plate of the piezoelectric stack in the axial
direction towards the strut end. The output elements of the
mechanical frame form the power transmission means from the
piezoactuator to the strut. The hereby considerably enlarged strut
distance between the resting areas of the two output elements
exhibits less stiffness, consequently leading to the fact that for
the expansion of this strut section less force is sufficient than
in a comparable configuration of a piezoactuator where the distance
of the resting surfaces of the output elements largely corresponds
to the length of the piezoelectric stack. The piezoelement also
uses the d33 piezoelectric elements.
[0011] Based on the drawing, exemplary designs of the invention are
explained in more detail in the following. It shows:
[0012] FIG. 1 an expansion actuator in a sectional view,
[0013] FIG. 2 an expansion actuator with stroke speed
transformation,
[0014] FIG. 3 an alternative version of an expansion actuator with
stroke speed transformation,
[0015] FIG. 4 a diagram of a strut with axially spaced output
elements of a piezoactuator,
[0016] FIG. 5 a sectional view of a strut with collar-shaped output
elements of a piezo actuator, and
[0017] FIG. 6 an alternative design of the output element with
recesses.
[0018] The expansion actuator 1 shown in FIG. 1 is rigidly fastened
to the surface of a structure 7 and consists of a d33 piezoelectric
stack 2, two end plates 3, two output elements 4 and a prestress
element 6.
[0019] The d33 piezoelectric stack 2 is arranged in its mechanical
frame such that its expansion direction runs parallel to the
surface of the structure 6 in which the expansion actuator 1
transmits its piezoelectrically generated expansions. The d33
piezoelectric stack takes up 1/3 of the material volume of a d31
piezoelectric stack for equivalent active expansions.
[0020] In the design in FIG. 1 the mechanical frame is formed by
the two output elements 4, which are rigidly attached to the
structure 6. To accomplish this, the output elements 4 are attached
in such a way to the surface of the structure 7 that their output
surface 5 is aligned parallel to the respective end plate 3 of the
piezoelectric stack 2. The output elements 4 can be fastened to the
structure 6 by means of familiar attachment techniques, for example
by gluing.
[0021] The output elements 4 can be adjusted on their attachment
surface to variously bent or plane structural surfaces. In the
design shown the structure is a pipe with a circular concave
surface. The length of the piezoactuator corresponds to the length
of the strut section that is supposed to be expanded.
[0022] The piezoelectric stack 2 is seated between its two end
plates 3 and held in place with a prestress element 6 at mechanical
precompression stress. Possible damaging tensile loads acting upon
the expansion actuator 1 are compensated with this precompression
stress and can thus have no effect on the piezoelectric stack
2.
[0023] The prestress element 6 can be implemented for example with
one or more mechanically acting tension springs--as indicated
symbolically in the design in FIG. 1. It is also possible, however,
to design the end plates 3 as elastic plates and to insert the
piezoelectric stack 2 with compressed end plates 3 into the
mechanical frame at precompression stress.
[0024] The expansion actuator 1 with stroke speed transformation
shown in FIG. 2 corresponds to the previously described design
except for the following deviations. The end plates 3 of the
piezoelectric stack 2 are not connected directly with the output
surfaces 5 of the output elements 4, but rather by means of an
elastic pressure web 8, and the output elements 4 comprise an
inwardly one-sided open slot 9 that runs parallel to the surface of
the structure 7. Furthermore, the two output elements 4 are rigidly
connected with each other by means of a non-expanding support bar
11, which engages in the free end 10 of the output elements 4. In
place of a support bar 11 two parallel support bars. 11 that are
arranged on either side of the piezoelectric stack 2 can be used,
as is revealed in FIG. 2 with a support bar 11 shown in the
drawing.
[0025] On each output element 4, the elastic pressure webs 8, slots
9 and support bars 11 form three joints "a", "b" and "c" about
which the lever sections of the output elements 4 can rotate and
generate a stroke speed transformation in the expansion actuator
1.
[0026] FIG. 3 depicts an expansion actuator 1 with stroke speed
transformation in an alternative design version compared to FIG. 2
of the output elements 4 and joints "a", "b" and "c". The effect of
lever sections about the joints "a", "b" and "c" in principle
corresponds to the previously described design in FIG. 2.
[0027] The output elements 4 here are designed with a lever 12 that
is seated in joint "a". The joint "b", in which the piezoelectric
stack 2 engages with an output web 14, is arranged on the lever 12
with a first lever section 13 at a distance to joint "a".
[0028] Joint "c" is arranged on the lever 12 with a second lever
section 15 at a distance to joint "b". Joint "c" engages in the
support bar 11.
[0029] FIG. 4 shows a diagrammatic image of a strut 16. The strut
can be, for example, a steel pipe with a fastening loop that is
welded onto each end. Such a strut is used, for example, in a
quadruple setting in order to connect the main gearbox of the rotor
of the helicopter with the cellular structure of the cockpit of the
helicopter. The main gearbox is hereby located above the ceiling of
the cellular structure of the cockpit. The two components are
connected in 4 locations by a strut 16, respectively. The main
gearbox of the rotor is one of the main sources of noise generated
in the cockpit. Since the strut 16 is seated on the interface
between the main gearbox and the cellular structure, it is useful
if elastic dimensional changes are generated on the strut, which
can largely compensate the forces introduced via the strut. This is
effected, for example, through a controlled dimensional change
(expansion or contraction) of the strut 16 in the axial direction
X. The controlled elastic dimension change is implemented with the
piezoactuator 17, which initiates a dimensional change,
particularly a change in length in the axial direction X in a
certain section D of the strut. In the strut 16 pursuant to FIG. 4
as well two output elements 18, 19 are arranged per piezoelectric
stack. The output elements 18, 19, however, are not connected
directly behind the end plate 20, 21 of the piezoelectric stack 22
with the surface of the strut 16, but the resting surfaces 23, 24
of the output elements 18,19 are arranged at a distance to the end
plate 20, 21 of the piezoelectric stack 22 in the axial direction
X. The piezoelectric stack 22 does not have to rest directly on the
surface of the strut. The force that is generated by the
piezoelectric stack 22 is introduced into the strut 16 on the
resting surface 23, 24. This force effects an elastic dimensional
change in a section D of the strut 16 between the two resting
surfaces 23, 24.
[0030] The section D along the strut circumference comprises the
corresponding sectional spatial structure of the strut, in short
called section D. The elastic dimensional change there compensates
the vibration force in the strut 16, specifically in the area of
the interface of strut and cellular structure.
[0031] The piezoelectric expansion actuator 17 is formed by d33
piezoelectric elements, which are arranged in a piezoelectric stack
22. The two ends of the piezoelectric stack 22 are limited by the
end plates 20, 21. The output elements 18, 19 are arranged on said
end plates 20, 21. The power application point of an output element
18,19 on the strut 16 is arranged at a distance from the end plate
20, 21 in the axial direction X towards the fastening loop 160,
161. Gaining such a distance is associated with gaining a lever arm
that engages on both sides of the end plates of the piezoelectric
stack. One lever arm E, F each is formed by the output element 18,
19. The lever arms E, F increase the section D by their length
since originally section D corresponded only to the length of the
piezoelectric stack.
[0032] The tensile force, for example, that is generated in a
selection of the piezoelectric expansion actuator is introduced
into the strut via the output surface of the output element. The
section D located between the output surfaces 23, 24 of the strut
16 is thus exposed to a controlled dimensional change in an axial
direction X. This change represents an elastic dimensional change.
Compared to the previously described solution, this alternative
solution takes advantage of the lower rigidity of an enlarged strut
section. This increases the efficiency of power application of a
piezoactuator 17 considerably. It is, therefore, possible to use a
substantially smaller piezoelectric stack without having to accept
an efficiency loss.
[0033] Multi-axis influencing of the dimensional change of the
described section D of the strut 16 can be controlled as a function
of the piezoelectric stack's configuration along the circumference
of the strut.
[0034] The arrangement shown in FIG. 4 can be also designed in the
inside of a tubular strut.
[0035] As FIG. 4 also shows, this elastic dimensional change of the
section D is controlled with a control unit 25. In the area of each
output element 18, 19, preferably in the vicinity of the resting
surface 23, 24, the control unit comprises a sensor 26, which
determines a signal from the quantitative value of the existing
vibrational forces and supplies it to the control device. The
control device 25 regulates the piezoelectric stack 22 such that a
force is generated by the piezoelectric stack and is introduced
into the strut 16 via the output elements 18, 19 so as to affect an
elastic dimensional change of the strut section D.
[0036] The distance D between the resting surfaces 23, 24 can be
implemented in a variably adjustable manner by designing at least
one lever arm E, F such that it can be enlarged and reduced.
[0037] The above explanations apply similarly to the piezoactuator
170 in FIG. 4 with the output elements 180, 190 and the
piezoelectric stack 220 with the end plates 200, 210.
[0038] FIG. 5 shows a sectional view of an design for a strut 30,
wherein the two fastening loops on the ends of the strut 30 are not
depicted.
[0039] FIG. 5 depicts three piezoelectric stacks 31, 32, 33, which
form a piezoactuator 34 along with the output elements 35, 36.
These piezoelectric stacks 31, 32, 33 are offset from each other,
for example, by 120.degree.. Each piezoelectric stack can be
arranged at a distance from the surface of the strut. The stacks,
however, can also be arranged on the surface of the strut 30. The
first version is shown in the example.
[0040] The axial axis of the piezoelectric stack is aligned in the
direction of the axial axis X of the strut 30. Each piezoelectric
stack is arranged between two output elements 35, 36. The two
output elements 35, 36 engaging one piezoelectric stack 31, 32, 33,
respectively, contain each an annular socket 37, 38, which encloses
the strut 30 in an interlocking and non-positive manner along its
circumferential surface. Extending from the annular socket 37, 38
the output element 35, 36 opens up in a bell-shaped manner like a
collar, which is arranged at a distance from the strut starting
from the edge of the annular socket to its annular edge. This shape
is described as an annular collar 39, 40. On the edge 41 of the
collar 39 rests one end of the piezoelectric stack 31, 32, 33,
respectively. The other end of the three piezoelectric stack 31,
32, 33 is respectively located on the edge 42 of the collar 40.
[0041] The annular socket 37, 38 of the collar 39, 40 exhibits
sufficient rigidity and firmness that corresponds to a resting
surface 370, 380 which is connected with the surface of the strut
30 in the circumferential direction in an interlocking and
non-positive manner. The forces generated by the piezoelectric
stacks 31, 32, 33 are introduced via the resting surfaces 370, 380.
Such a design for an output element 35, 36 permits action in a
variety of spatial axes. Hence more variable design possibilities
exist for introducing power into the strut 30. The forces and
bending moments that are introduced into the strut 30 can be used
to effect an excursion in the longitudinal (axial) direction, a
lateral bending excursion in any random direction and also torsion
of the strut 30.
[0042] This elastic dimensional change also affects a structural
region in the strut 30 along section D.
[0043] By using at least two piezoelectric stacks that are arranged
around the strut, the strut can be displaced in the longitudinal
and lateral directions through appropriate selection of the
individual piezoelectric stacks. A suitable control or regulating
device is not shown in FIG. 5.
[0044] It is also possible to introduce torsional forces by
inserting the piezoelectric stack at an angle, i.e. a configuration
of at least one piezoelectric stack that is tilted in relation to
the longitudinal axis X of the strut 30.
[0045] FIG. 6 depicts another possible design of an output element.
It is shown as a single output element 360 without strut and
without piezoelectric stack. The output element 360 is guided in
the direction of the axial axis X of a strut and fastened to the
surface of the strut by means of its annular socket 390. A collar
400 is incorporated on the annular socket. This collar 400 contains
recesses 401 so that weight of the output element can be saved. The
collar 400 includes for example three arms, which can be arranged
at an angle of 120.degree. in relation to one another. These three
arms of the collar 400 are connected and limited at their ends by a
ring 420. This ring 420 forms the edge of the collar 400. One end
of a piezoelectric stack is arranged on the edge of the collar,
respectively.
[0046] Pursuant to another design (not shown), it is also possible
to divide an output element 360 partially into sectional output
elements. To accomplish this, sectional output elements are
arranged in a non-positive manner with each other in one direction
along the circumference of a strut in segments and are connected.
In the viewing direction of the X-axis, an output element can be
divided into individual (wedge-shaped) segments, which are arranged
around the X-axis. The output element is thus composed in segments
of sectional output elements. The output element pursuant to FIG.
5, for example, could be composed of three sectional output
elements in the case of three piezoelectric stacks. This
configuration of sectional output elements is an easy option for
retrofitting a strut on the helicopter that has already been
installed.
[0047] Such a configuration makes it possible to reduce the
vibrations generated by the main gearbox in relation of the
cellular structure of the cockpit efficiently for the pilot and
noticeably for the passengers.
* * * * *